Increased vapor generator output feature



Dec. 23, 1969 a. s. MILIARAS INCREASED VAPOR GENERATOR OUTPUT FEATURE Filed June 28, 1968 2 Sheets-Sheet 1 E. S. MlLlA-RAS INCREASED VAPOR GENERATOR OUTPUT FEATURE Dec. 23, 1969 2 Sheets-Sheet 2 Filed June 28, 1968 United States Patent 3,485,048 INCREASED VAPOR GENERATOR OUTPUT FEATURE Emmanuel Stephen Miliaras, 12 Mount Pleasant St., Winchester, Mass. 01890 Filed June 28, 1968, Ser. No. 740,919 Int. Cl. F22g /00, 7/14; F22d N00 US. C]. 60-70 12 Claims ABSTRACT OF THE DISCLOSURE This invention relates to methods for increasing the output of a vapor generator, with some decrease in efiiciency, by additional heat input ahead of the economizer for the purpose of meeting demands often of limited duration, as for example in producing additional steam for a turbogenerator to satisfy peaking type electrical loads in the case of a utility steam generator.

tinuous operation.

The acceptable gas pressure drop across the economizer is also a design factor and the relatively small temperature differential between the fluids involved in the heat transfer results in a low figure for the heat absorption for the economizer surface.

The limit on the temperature of the feedwater entering the economizer is determined by the need for complete deaeration of the feedwater; the economizer exit temperature is often below the temperature of producing steam at that pressure or is determined by tube temperature restrictions, sometimes downstreams of the economizer. The lower limit of the gas temperature leaving the economizer is often determined by the need for the departing gases to be above the dew point. The temperature design limits and stresses in the boiler tubes are determined on the basis of creep strength and occasionally can be exceeded for limited intermittent operation.

In power generation, short term electrical demand is often met by shutting off feedwater heaters, operating at overpressure or by-passing excess steam to the turbine downstream of the first stage.

Of the three main components of a fossil fuel power plant the turbine offers considerable above rating capability at small additional cost in plant investment and the condenser can also accommodate overloads with some detriment to eificiency; only the steam generator, by current design considerations, is limited in carrying overloads,

beyond the manufacturers designed continuous rating.

The invention is directed to means for increasing the output of a vapor generator, by providing additional heat input for the economizer; the invention relates to existing vapor generator designs and also to future designs where the means for increasing output have been incorporated or allowed for in the design for future utilization, with consequent allowance in the design by judicial selection of heat transfer areas in the vapor generator components, materials choice, temperature design limits and piping and auxiliary equipment sizing for the integral plant, to better utilize the additional vapor generator output.

The means for obtaining the additional vapor generator output are set forth below and described with reference to the following figures:

FIGURE 1 is a diagrammatic illustration of a vapor generator embodying the present invention and FIGURES 2 and 3 are views similar to FIGURE 1 illustrating different means for introducing heat for the economizer.

The vapor generator comprises a furnace 6 and flue gas path enclosure 7 (both of which may be, subdivided), lined with closely spaced water cooled or water and steam cooled tubes 8, fuel burners 9, steam superheating tube bundles 10a, resuperheating tube bundles 10b, and economizer tubes 12.

In FIGURE 1 additional fuel is burned in refractory lined duct 13 adjacent to and communicating with the gas path enclosure and the hot products of combustion discharged ahead of the economizer. The additional fuel is introduced through burner 14 and combustion air is provided through fan 15 drawing air from the ambient or by a connecting duct to the main forced draft fan discharge duct. Damper 17 is closed when the increased vapor generator output feature is not in use.

The additional combustion may alternatively or additionally take place in the space directly ahead of the economizer in the gas path enclosure, the fuel being introduced through burner 16, to the extent that the remaining oxygen in the gases leaving the furnace will allow when operating with high excess air to the furnace, or by introducing additional combustion air and/ or oxygen with the additional fuel.

In FIGURE 2 additional combustion takes place in the adjoining gas path enclosure duct 18, by introducing fuel and combustion air at burner 19, similarly as in FIG- URE 1, except that partial recirculation of the gases in the gas path enclosure mixed with the additional combus tion gases is established around the economizer by fan 20, whose suction is connected by duct ;21 to the gas path enclosure downstream of the economizer, the heat transfer to the economizer tubes benefiting from the increased gas mass flow. Dampers 22 and 23 are used for controlling the recirculating gas flow and also to isolate the adjoining combustion duct from the gas path enclosure when the increased vapor generator output feature is not in use.

In FIGURE 3, excess hot combustion gases, generated in the furnace by additional fuel firing, are carried through refractory lined duct or ducts 24, communicating with the furnace through several openings, to openings in the gas path enclosure upstream of the economizer (by-passing superheating and resuperheating tube bundles) and mixed with cooler combustion gases raising the temperature and mass flow of the gases flowing past the economizer tubes and thus increasing the heat input to the economizer. The gas flow through duct 24 is made possible on account of the lower pressure existing in the region upstream of the economizer in relation to the furnace; the said gas flow is assisted where required by jet pump action, the higher pressure" fluid in the jet pump being cooler combustion gases taken through duct 25 from region downstream of the economizer, or ambient air, and raised in pressure by fan 26; the lower pressure fluid in the jet pump is the said excess combustion gases flowing from the furnace through duct 25a. Dampers 27, 28 and 29 control the gas flow through the respective ducts and remain closed, isolating the furnace from the gas path enclosure when the increased vapor generation feature is not in use.

The operation of the vapor generator utilizing the invention is envisaged along the following lines:

When the vapor generator is operating below or at rated output, the dampers to the ducts for the circulation of the additional combustion gases will be closed, no additional combustion will take place and the machinery assisting the movement of the additional combustion gases will not be operating. The efficiency of the vapor generator will be unaffected by the presence of the increased vapor generation features.

When the increased vapor generation is desired, the dampers to the ducts for the movement of the additional combustion gases will be opened, the machinery for the movement of the additional combustion gases will be operated, additional combustion will take place to the extent required for the increased vapor generator output, the amount of additional combustion air and additional combustion and recirculated gases to be regulated by the position of the dampers and the output control features of the machinery assisting the movement of the gases. The draft to the furnace will also be adjusted to the new gas flow pattern requirements and the feedwater flow adjusted to the increased vapor generator output.

The efficiency of the vapor generator will decrease as the combustion gases will be leaving the furnace at a higher temperature.

An application of the invention is illustrated in FIG- URE l, where 30 is a high pressure turbine section, 31 is a lower pressure turbine section receiving reheated steam, 32 is the electrical generator coupled to the turbine, 34 designates the condenser, 35 are closed feedwater heaters, 37 are valves controlling the steam extraction flow to the heaters, 36 is a deaerating heater, and 38 is a system electrical demand sensor and generation dispatching device.

A portion of the increased vapor generator output, produced on account of the increased heat input to the economizer, according to the invention, is throttled through valve 33, by-passing the high pressure turbine section 30, and in this case the reheater b, and joins the reheated steam, approximately at the same pressure and temperature, on the way to the lower pressure turbine section 31.

The utilization of the increased heat input to the economizer is also considered in connection with the practice of temporarily and for a short period shutting off the steam supply to the highest pressure feedwater heater in order to increase the steam flow through the turbine, and thus the electrical output of the turbogenerator. The feedwater entering the economizer is then at a lower temperature and, as additional heat input is required to the vapor generator, the shutting off of the steam supply to the feedwater heater is of limited duration. The invention,

by providing for additional heat input to the economizer,

allows for increased electrical output by shutting off the steam supply to several feedwater heaters, with the exception of the deaerator, and increasing the steam flow through the turbine; the deaerator, on account of the deaerating function, is essential for the removal of oxygen from the feedwater.

The operation of the embodiment of FIGURE 1 may be as follows. Upon receipt of an incoming signal by device 38 that electrical demand is increasing and the increased output feature of the generating unit is called upon to provide additional output, outgoing signals will be generated by device 38 to close valves 37 to the feedwater heaters 35, thus increasing steam flow through the turbine, open damper 17, operate fan 15, and fire additional fuel through burner 14 (and/or 16) increasing heat input to the economizer which, after shutting off the steam supply to heaters 35, will be receiving feedwater of lower temperature and, upon indication to the sensing device 38 or other instruments or computing devices that vapor generator output is increasing, open valve 33 to provide additional steam to the lower pressure turbine 31.

In developing the invention, the intent has been to provide increased vapor generation, by additional heat input to the economizer, with small expenditure for additional equipment, to take advantage of the known overload capabilities of the turbine and the condenser, in order to increase the electrical generation of a power plant, at some loss in efficiency, for the purpose of meeting peaking type electrical demand.

The terms and expressions which have been employed in presenting the invention and its embodiments are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding equivalents of the features shown or described therein; but is recognized that various modifications and combinations of the features mentioned are possible or desirable, as the constraints of an existing vapor generator modified to utilize the invention will dictate, or the engineering and economic optimization of future vapor generator designs to utilize the invention will indicate.

Other embodiments will be apparent to these skilled in the art and are within the following claims:

What is claimed is:

1. In combination with a fossil fired vapor generator having a given designed continuous rating, a secondary system adapted to increase the steam output of said generator above said rating under peak demand conditions, said steam generator comprising a vapor generator section, a superheating section and an economizer section, a flue gas flow passage defining a flue gas flow path successively from said vapor generator section through, said superheater section and said economizer section, water passages introducing feedwater to said economizer and conducting water from said economizer to said vapor generator section, and steam passages for conducting steam from said vapor generator to said superheater and from said superheater to an output line, and said secondary device comprising supplementary heated gas means, including an inlet located in said flue gas flow path between said superheater section and said economizer section and means for electively operating and securing said supplementary heated gas means, said supplementary heated gas means constructed and arranged to provide in said flue gas flow-path supplementary hot gaseous combustion products, whereby the flue gases flowing from said superheater section and said supplementary hot gaseous combustion products together, in flowing through said economizer section, can increase the heat input to water flowing through said economizer at peak demand, above the economizer heat input that corresponds to the continuous rating of said steam generator.

2. The combination of claim 1 wherein said inlet comprises a supplementary fossil fuel firing burner adapted to discharge fuel into the flue gas path between said superheater and economizer sections, said flue gas path including a combustion region in which fuel from said supplementary burner burns.

3. The combination of claim 1 wherein said inlet comprises at least a first supplementary gas duct connected to introduce supplementary hot gaseous combustion products for flow through the economizer section.

4. The combination of claim 3 including a supplementary fossil fuel firing burner connected to discharge fuel into a supplementary combustion chamber connected to said supplementary duct.

5. The combination of claim 4 including a gas blower connected to discharge into said supplementary combustion chamber, a second supplementary duct furnishing gas to said blower, said second duct connected to receive flue gas from the flue gas flow path in the vicinity of said economizer.

6. The combination of claim 3 wherein said secondary system is positioned immediately adjacent said economizer section and includes a reverse flow path defined by said first duct and a second duct connected to discharge to said first duct, said second duct connected to the flue gas passage downstream of said economizer, said means for electively operating said secondary system including dampers arranged to close said first and second ducts from communication with the line gas passages of said vapor generator.

7. The combination of claim 3 wherein said secondary system includes a reverse gas flow path including a second duct connected to the flue gas passage downstream of said economizer, and a chamber to mix gas withdrawn through said second duct with hotter gas from a third supplementary duct, said chamber connected to discharge through said first duct for flow through said economizer.

8. The combination of claim 7 including a blower connected to receive flow from said second duct and to produce a jet of said gas, said third duct connected to the furnace of said vapor generator preceding said superheater section, said third duct connected to introduce gases for suction by said jet and said first duct connected to receive the combined flow from said second and third ducts and introduce it to flow through said economizer, and said means for electively securing said secondary system including dampers arranged to close said first, second and third ducts from communication with the furnace and the flue gas passages of said vapor generator.

9. The method of operating a fossil fired steam generator that comprises a vapor generator section, a superheater section and an economizer section, gas flow passages defining a gas flow path successively through said vapor generator section, said superheater section and said economizer section, water passages introducing feed water to said economizer section and conducting water from said economizer to said vapor generator section and steam passages for conducting steam from said vapor generator to said superheater and from said superheater to an output line, comprising, upon the existence of a peak demand condition, providing, in the flue gas flow path between said superheater and economizer, supplementary hot gaseous combustion products in addition to those products received from the superheater to increase the heat input rate of said economizer.

10. The method of claim 9 used with a steam generator having in addition a feedwater heater preceding said economizer and a steam line introducing turbine extracted feedwater heating steam into said heater, comprising the further step of reducing the steam flow to said heater while providing said supplementary hot gaseous combustion products to said flue gas path.

11. The method of claim 9 used with a steam generator combined with an electric turbogenerator having a high pressure turbine and a low pressure turbine and including a superheater portion and a resuperheater portion, the output line of said superheater portion connected to the inlet of said high pressure turbine, the out put line of said high pressure turbine connected to the inlet line of said resuperheater portion and the output line of said resuperheater portion connected to the inlet of said low pressure turbine, comprising the further step of throttling a portion of the flow from said output line of said superheater portion through a throttle valve into the inlet of said low pressure turbine while providing said supplementary hot gaseous combustion products to said flue gas path.

12. The method of claim 9 used with a steam generator having in addition a feedwater heater preceding said economizer, a steam line introducing turbine extracted feedwater heating steam into said heater, a high pressure turbine and a low pressure turbine, a superheater portion and a resuperheater portion, the output line of said superheater portion connected to the inlet of said high pressure turbine, the output line of said high pressure turbine connected to the inlet line of said resuperheater portion and the output line of said resuperheater portion connected to the inlet of said low pressure turbine, comprising the additional steps of reducing the steam flow to said feedwater heater and also throttling a portion of the flow from said output line of said superheater portion through a throttlevalve into the inlet of said low pressure turbine while providing said supplementary hot gaseous combustion products to said flue gas path.

References Cited UNITED STATES PATENTS KENNETH W. SPRAGUE, Primary Examiner US. Cl. X.R. 122-477, 479 

